An introduction to Hydrozoa

Hydrozoa occur in all aquatic habitats. They form part of the plankton, the hard- and soft-bottom macrobenthos, and the meiofauna. They can also be symbiotic with a wide variety of animals and plants, and some are parasitic. Some hydrozoans are famous experimental animals, such as Hydra and Hydractinia. The presence of polyp and medusa stages in the life cycle of many species led to a double taxonomy that is being unified through a research project that started in the first half of the last century and is still continuing. The present monograph assembles the most relevant knowledge on the group, with a list of all the known species and diagnoses of all supraspecific taxa. This is an intermediate step towards the appreciation of the diversity of the Hydrozoa, the aim being to attract the curiosity of biodiversity students and to motivate them to fill the many gaps that remain in our knowledge of this fascinating group. The authors are all members of the Hydrozoan Society and this book is a product of the philosophy of the Society.

Jean Bouillon dedicated his life to the study of the Hydrozoa, starting with life cycles, histology, developmental biology and evolution, culminating his career with the description of more than 150 new taxa, from species to orders. He established the core of this book. Cinzia Gravili studies life cycles and taxonomy of the Hydrozoa. She has assembled a monumental database on the literature of the group. She worked on the nomenclatural and bibliographic aspects of this book. Francesc Pagés specializes in the taxonomy and ecology of planktonic hydrozoans, with particular focus on the Siphonophores: he is the main contributor for this group in this treatise. Josep-Maria Gili works on both planktonic and benthic Hydrozoa. His interests range from taxonomy to ecology and he contributed to the monograph by taking care of these aspects. Ferdinando Boero works on taxonomy, life cycles, ecology and evolution of the Hydrozoa and contributed to these themes in the writing of this book.